Floating Point Gotchas

see forum discussion here: http://forum.dlang.org/post/oxadmevgkefklttnbbpi@forum.dlang.org

Floating point comparisons should be undertaken with care, because decimal numbers cannot be exactly represented using float or double. The classic reference on this topic is here:

http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html

One should therefore in most cases use std.math.feqrel and or std.math.approxEqual instead of checking for simple equality.

These functions may be passed as a predicate to the std.algorithm library in Phobos when for example doing a search for a specific floating point value:

void main() @safe {

   import std.stdio, std.range, std.algorithm, std.math;

   immutable float oneDegree = (PI / 180.0f);
   immutable float first = -(oneDegree * 10.0f);
   immutable float second = (oneDegree * 10.0f);
   immutable float step = 0.000001f;
   immutable float[] r = iota(first, second, step).array;

   //r.writeln;

   immutable float item = 0.174531f;
   r.canFind!q{ feqrel(cast()a, cast()b) >= 21 }(item).writeln;

}